For the past few days, I've noticed that both of my Android TV devices (one's a MiBox S, the other a Hisense H8G) are available to add to a speaker group. I went to cast something to my group "The House" and noticed that a volume slider for my Hisense was available with my 2 Home Minis, so I added the MiBox in and it also works.
I'm enrolled in the Chromecast built-in beta program, so this could have something to do with it. It's a bit moody at times, where I have to disconnect and re-cast until playback finally starts working. But I'm not complaining, I don't care to fidget with it since I've at least got the option.
The only issue, once it's connected properly, is that the audio delay initially is off by around 200ms, even with group delay set, but it does eventually correct, or I can manually adjust the group delay to reset it. Other than that, I've been enjoying playing music across all of my devices!
Does it work for anyone else?
Yep, was able to add my CCGTV back to my Speaker group.